In the United States the Federal Communications Commission (FCC) and National Telecommunications and Information Administration (NTIA) jointly regulate the civilian and non-civilian use of radio frequency bands of the electromagnetic spectrum, respectively. An aspect of radio frequency regulation is to declare which type of user shall receive exclusive or priority access to a frequency band and among co-equal users which type of wireless service shall be prioritized. This process is called allocation and through it a hierarchy of primary and subordinate (e.g. secondary) users and services is established.
In a given radio frequency band civilian use may be allocated primary over non-civilian use, which would be allocated secondary. In another frequency band allocation non-civilian use may be primary over civilian use; in yet another band both uses may declared co-primary, and so forth. For example, in the 219-220 MHz band civilian use is allocated primary and among civilian users fixed and mobile land radio service is allocated primary while amateur radio service is declared secondary.
In the United States, radio frequency band allocation is negotiated between the NTIA and FCC. In other countries the national telecommunications regulator typically maintains a similar responsibility.
In a wireless communications system an Incumbent User (IU) is generally defined as either a user having primary status over another (e.g. secondary) user or, in the case of co-primary users, a wireless service type having primary status over another (e.g. secondary) service having. It may also occur in certain frequency bands that additional levels of prioritization are established by the regulator, such as, for example, a tertiary, quaternary, quinary, etc. user or service.
A regulator may undertake to reallocate a radio frequency band from time to time to allow co-primary use between civilian and non-civilian users or to allow civilian secondary use of a band in which civilian use was previously prohibited. When such a reallocation occurs it may develop over time where the introduced secondary users grossly outnumber the incumbent users and a spectrum sharing authority is required to coordinate spectrum sharing and to protect the incumbent service from radio frequency interference (RFI) from secondary users. Occasionally, and more frequently in recent years, a plurality of privately operated Spectrum Access Systems (SAS) may be designated by a regulator to operate as a spectrum sharing authority.
In certain circumstances a non-civilian incumbent user does not or may not inform the SAS about its spectrum operations. In this case the SAS may be supplemented by a separate Environmental Sensing Capability (ESC) that detects the incumbent user. In this context the term “Environmental Sensing Capability” (and abbreviated to ESC) means a distributed system of radio frequency sensors and the term “ESC” is therefore not used as a generic capability to detect but rather as the actual system doing the detection.
As an example, this is precisely the case in the 3,500-3,750 MHz frequency band where the allocated primary user is the U.S. Military, which is a non-informing incumbent whose spectrum operations are non-public and subject to security constraints.
Accordingly, there is a need to detect and also to protect non-informing incumbent users in a manner that satisfies the incumbent user's operational security and information security requirements.